1. Field of the Invention
The present invention relates to a method and apparatus for testing clutches and bands in a vehicle transmission, and more particularly relates to a method and apparatus for testing a vehicle transmission which enables a technician to test the transmission unit under fluid pressure to simulate normal operating pressure conditions while the transmission is actually at rest in a non-running condition, whether the transmission is installed in the vehicle or removed for rebuilding or repairs.
2. Description of the Prior Art
Numerous transmission testing devices have been provided in the art for testing the working parameters of a transmission. These devices are adapted for coupling to the transmission housing and are usually constructed to include test plugs on the exterior to provide a means to operatively engage the test device to the transmission. These test devices enable technicians to determine the conditions at a particular band or clutch combination, and generally provide for analysis of the transmission only while the vehicle engine is running or under conditions simulating normal running condition. The problem with this type of test apparatus is that the data which the test yields is pure result with no indication of the cause, and while a technician may determine that a problem exists, the cause of the problem still must be further investigated, usually in furtherance of the trial and error method employed with these devices.
Identifying the cause of a problem using these prior art methods and devices generally requires additional and elaborate "process of elimination" diagnostic procedures because there is no means to attempt to isolate the individual components of the transmission for separate evaluation. It is most often impossible to correctly identify an internal condition or problem in the transmission in this way.
Internal components, such as the clutches and bands within the transmission, may be tested and analyzed based on the amount of fluid pressure applied and the ability of these parts to hold the pressure. The working life of the transmission itself can be predicted in part by the amount of fluid pressure which each individual clutch/band is able to maintain after application and initial leakdown.
While these devices may be suitable for the particular purpose to which they address, they would not be as suitable for the purposes of the present invention as hereinafter described.
U.S. Pat. No. 3,967,495 to Wesner et al. discloses a diagnostic instrument for detecting and locating malfunctions in a pneumatic circuit such as the circuit which controls a transmission in response to movement of an operator shift lever. The instrument tests the pneumatic control circuit to determine if appropriate pressures are present at key points as required along the various points in the circuit. Compressed air is supplied through the test instrument to test the circuit between the shift lever and the transmission. This type of device does not test the clutches and bands of the transmission itself, but rather uses compressed air to test the pneumatic lines between the shifting mechanism and the transmission. A specific disadvantage of this system exists in the use of compressed air to test the pressure at various points in the control circuit. Minute leaks may go undetected, and while the gauges may be sensitive enough to indicate a pressure drop corresponding to a leak in the line, it may be impossible to pinpoint the location of the leak since only air will be emitted from the leaking location. Furthermore, it is apparent that this testing instrument is for use on a transmission that has been removed from a vehicle and the transmission must be operated to simulate conditions of normal operation.
U.S. Pat. No. 4,356,724 to Ayoub et al. discloses an apparatus and method for testing transmissions that have been removed from the vehicle. A base is provided to receive the transmission and the transmission is operated to simulate normal operating conditions to test whether the transmission is shifted within the prescribed limits set by the manufacturer of the transmission. Variable speed drive means are provided for rotating the input shaft of the transmission under test and a load means is provided to load the output of the transmission during the test. Fluid pressure is monitored by a pressure sensor and an input speed sensor and an output speed sensor are provided for monitoring the input and output speed.
U.S. Pat. No. 2,918,822 to Mann, Jr. discloses a test bench and apparatus for testing automatic transmissions that have been removed from a vehicle. Pressure gauges may be provided to determine pressure within the transmission, and the transmission is operated to simulate normal operating conditions during operation of the test. This device is used primarily to check the complete shift pattern of the transmission to test for slippage between the shafts.
U.S. Pat. No. 3,273,384 to Flaugher discloses a device for testing an automatic transmission of a car that is mounted within the vehicle. The test device includes a series of rollers so that the vehicle may be operated in a normal manner so that the wheels actually rotate and the transmission is driven in a normal manner. The device may also be connected to the vehicle so that the vehicle may be road tested while the transmission is being tested.
U.S. Pat. No. 3,213,674 to Salcido et al. discloses a tool for testing fluid tight seals such as the clutch plate seals in clutch drums of automatic transmissions of automobiles. Air or hydraulic fluid may be admitted under pressure to the individual clutch plate to test for leakage of the clutch plate seals. It is apparent that the clutch plate must be removed from the transmission prior to testing using this device, and it is apparent that the transmission must be disassembled to facilitate use of this tool.
The novel apparatus for testing clutches and bands within an automatic transmission of the present invention obviates the disadvantages of the prior art and provides an efficient and easy to use testing instrument which allows for quick, accurate testing of a transmission whether the transmission is mounted in a vehicle or removed from the vehicle for repairs. The device controls the flow rate of a fluid which travels through the device to determine the percentage of leakage or retention of pressure within each individual clutch or band of the transmission which is under test. The transmission is testing in a static, non-operating condition, which allows the transmission to be tested in the vehicle without having to operate the vehicle, but at the same time testing for leakage or deterioration of each individual band and clutche.